Superconducting current accumulator with pulsed output

ABSTRACT

A process for supplying a current consumer with current from an accumulator for electrical energy, in which electrical energy pulses of very short duration each are supplied to the current consumer from a superconducting accumulator (2) made with superconductors (8) of very small diameter or very small layer thickness. The superconductors (8) are preferably high-temperature superconductors.

BACKGROUND OF THE INVENTION

The invention relates to a process for supplying a current consumer withcurrent from an accumulator for electrical energy, well as to a currentaccumulator suitable for carrying out said process.

The design and procedure of current delivery prevailing so far incurrent accumulators have been such that a current accumulator deliveredthe required energy in a continuous or quasi-continuous manner over arelatively long period of time.

SUMMARY OF THE INVENTION

The object to be met by the invention is to make available a process forsupplying to make available a consumer with current from a currentaccumulator, as well as a current accumulator having a high storagecapacity in relation to volume or weight, while enabling storage withextremely low losses and enabling also discontinuous current delivery.

To meet this object the process, according to the invention, ischaracterized in that electrical energy pulses of very short durationeach are supplied to the current consumer . from a superconductingaccumulator coil composed of superconductors of very small diameter orvery small layer thickness. The current accumulator according to theinvention is characterized in that it is designed as a superconductingaccumulator coil having superconductors of very small diameter or verysmall layer thickness.

The invention thus teaches the use of a superconducting accumulator coilof such construction that the energy delivery is possible in the form ofvery short energy pulses, and with extremely low eddy current losses.

Especially suitable small diameters or small layer thicknesses of thesuperconductors are less than 20 μm, preferably less than 10 μm.Especially suitable short periods of time of the respective energypulses are less than 10 ms, preferably less than 5 ms and mostpreferably less than 1 ms.

A particularly preferred embodiment of the invention consists in makingthe accumulator coil with high-temperature superconductors.High-temperature superconductors are superconductors that are stillsuperconducting at considerably higher temperatures than thoseconsidered possible in principle until recently. As a handy limit forthese materials, one may indicate a transition temperature, i.e.temperature of the transition from the superconducting state into thenormally conducting state, of 80° K. It is typical that high-temperaturesuperconductors are still superconducting at a temperature slightlybelow the boiling point of liquid nitrogen. Typical materials forhigh-temperature superconductors are ABa₂ Cu₃ O₇ (wherein A=YLa, Nd, Sm,Eu, Gd, Ho, Er, Lu as well as Y₁.2 Ba₀.8 CuO₄. Another example is La₁.85Sr₀.15 CuO₄, is to be indicated as which has a transition temperature ofapprox. 40° K. and is not a high-temperature superconductor according tothe above definition. These materials usually are so-called layerconductors or two-dimensional superconductors. High-temperaturesuperconductors are known per se, just as conventional superconductors,whose transition temperature is in the rang of several degrees Kelvin,and there is no need for indicating more concrete examples in thisrespect, since these are generally known.

Despite the very short energy pulse duration preferably employed fordischarging the accumulator coil according to the invention, high energyor power delivery is possible because of the considerable energy contentper energy pulse and because of the large number of possible successiveenergy pulses. Typical values are more than 10₈ W per energy pulse,preferably 10⁸ to 10¹¹ W.

The small diameter or small layer thickness of the superconductors ofthe accumulator coil, provided according to the invention, has theeffect that the eddy current losses in the superconductors are kept aslow as possible also in case of an energy delivery in the form of veryshort energy pulses in terms of time. Possibilities of manufacture ofsuch superconductors, which are preferred according to the invention,are vacuum evaporation, local mechanical removal or etching of portionsfrom a layer of larger area, as well as winding of the accumulator coilfrom very thin wires, so-called filament wires. Not only winding butalso evaporation and local layer removal provide the possibility ofhaving, when viewing an accumulator coil cross-section, severalsuperconductors or superconductor rings on top of each other in theradial direction so as to increase the storage capacity per unit oflength of the accumulator coil, for instance by repeated evaporation orrepeated layer application and repeated material removal. Between theindividual superconductor layers there are usually disposed insulatingintermediate layers which, for instance, may be formed by evaporationand may consist, for instance of aluminum oxide. Such manufacturingtechniques may be performed such that the radially successive layers orcoatings electrically provide a winding-like structure. However, interms of manufacture it is often more convenient to form ring-likelayers or coatings and to electrically contact or terminate eachthereof. In case of a winding structure of the accumulator coil it ispreferred to wind the superconducting filament wires in an alternatingmanner with very thin normal-conduction metal wires. Thenormal-conduction metal wires appropriately should be at least as thinas the superconducting filament wires, so as to keep the eddy currentlosses as low as possible also in the normal-conduction wires. The term"in an alternating manner" is not to be understood only in the strictsense of the word. Rather, what is to be expressed is that the aim is amatrix-like structure partly of superconducting and partly ofnormal-conduction filament wires, without the cogent requirement thatone superconducting filament must cogently alternate exactly with onenormal-conduction wire. The result of this structure is that, even incase of a breakdown of superconduction in the superconducting filamentwires, at least the normal conduction in the normal-conduction wires isstill maintained

As a further development of the invention, it is particularly preferredwhen the accumulator coil is composed with several successive coilsegments in the longitudinal direction of the accumulator coil. It iseven possible to separately prefabricate the individual coil segmentsand to then join them to form the accumulator coil. These measuressimplify the structure and the manufacture of the accumulator coil.Besides, it is possible in a particularly simple manner, according tounit construction principles, to selectively build accumulator coilswith smaller or larger storage capacity. However, it is possible as wellto manufacture the entire accumulator coil as a whole, for instance towind the coil with a continuous superconducting filament wire on a coilcore.

When a structure of coil segments is used, it is preferred for reasonsof simplification that the coil segments are magnetically coupled witheach other and have, for instance, a common coil core. However, anelectrical interconnection of the coil segments is possible as well.

A construction of the accumulator coil of coil segments provides thepreferred possibility of interconnecting part or all of the coilsegments for charging the accumulator coil and/or of having a differentinterconnection of the coil segments for charging and for discharging,with the coil segments active during charging being not necessarilyidentical with the coil segments active during discharging. Aparticularly preferred possibility consists in charging the accumulatorcoil using a series connection of part or all of the coil segments andin discharging it using a parallel connection of part or all of the coilsegments. In this manner, upon discharge of n coil segments, one obtainsthe n-th discharging current of one individual coil segment.Furthermore, it is possible by means of switching components to renderselectable the number of coil segments which are directly cooperatingduring discharge, so that the magnitude of the discharging current canbe adjusted in this simple manner. The charging current is as a rulesubstantially unchanged.

It is possible to interconnect several magnetically coupled accumulatorcoils, especially for discharge.

The easiest possibility for charging the accumulator coil consists inconnecting it to a primary current circuit. Alternatively or in additionthereto it is possible, and

preferred for many purposes of application, to charge the accumulatorcoil magnetically or inductively a charging means. Magnetic flow quantacan be introduced in the accumulator coil especially according to theflow pump principle, i.e. in a time-distributed manner in so small"portions" that the superconducting state of the superconductors doesnot break down. Preferred technical possibilities therefor are apulsating magnetic field, produced preferably by a rotatable magnet ringwith permanent magnets, or a pulsating field of a current conductor,which leads to the inductive introduction of magnetic flow quanta. It ispossible to use the rotating mass of the magnet ring in addition toenergy storage. The magnet ring is driven preferably mechanically or byan electric motor, and particularly is driven directly. Charging of theaccumulator coil may be carried out by means of a flywheel accumulator,either in such a form that the afore-mentioned magnet ring is part ofthe flywheel of the flywheel accumulator which is charged preferably byan integrated electric motor with increasing speed, or in such a formthat electric current produced in the generator mode of operation of theflywheel accumulator is fed to the accumulator coil.

The preferred geometric configurations of the accumulator coil are atoroidal configuration (=annularly curved hollow cylinder) and solenoidconfiguration (=hollow cylinder). The toroidal configuration leads to aparticularly compact current accumulator and offers, furthermore,particularly favorable geometrical-functional conditions for charging inaccordance with the flow pump principle. As regards the toroidalconfiguration of the accumulator coil, the term "longitudinally of theaccumulator coil" used in the present text is to be understood such thatthis longitudinal direction extends circularly in a manner correspondingto the circular shape of the center axis of the coil.

Especially favorable conditions under the aspect of minimization of theedge effects of the coil are obtained when--as is preferred--the ratiobetween the radial thickness of the space equipped with superconductorsand the accumulator coil diameter is small. This means, depending on thedesired storage capacity of the accumulator coil, the diameter of theentire accumulator coil (in case of the toroidal configuration measuredwith respect to a cross-section of the toroidal ring) is made as greatas possible and the radial thickness of the coil proper or of the coilsegments proper is made as small as possible.

The accumulator coil may be designed as a coreless coil or air-corecoil. Preferably the accumulator coil is formed with a core composed ofsuperconducting material, in particular in the form or a layeredstructure alternating between insulating material and very thinsuperconducting layers. The core urges the magnetic field of the coil orcoil segments outwardly and thus leads to a magnetic fieldconcentration.

It is possible to alter or adjust the current intensity in theaccumulator coil by the transition of the material of the core from thesuperconducting state into the state of normal conduction, and viceversa. This can be achieved in principle by changing the temperature ofthe core, in particular by thermal energy irradiation. Particularypreferred is a means for applying a sufficiently strong magnetic fieldto the core, which does not interrupt the superconducting state of thecore. Further possibilities are the introduction of a sufficientlystrong current pulse or of an additional current pulse into the core,irradiation of a radio-frequency field into the core, subjecting thecore to the influence of a laser beam and/or subjecting the core to theinfluence of a maser beam. What must be noted on the whole is that thefield strengths and/or temperatures produced in the material of the coreof the accumulator coil shall not influence the desired superconductingstate of the accumulator coil.

The accumulator coil preferably has one or more superconductingdischarging coils magnetically coupled to the superconductors. These maybe coil segments of the accumulator coil proper. However, it is alsopossible to provide separate discharging coils between the windings orcoil segments proper of the accumulator coils. In doing so, atransformer effect can be utilized in case of differring windingnumbers.

The technical construction of the accumulator coil in most cases is suchthat at least the superconductors thereof are arranged in a helium bathor--in case of high-temperature superconductors--in a nitrogen bath. Theentire accumulator coil can be disposed in such a bath. In this case,the construction usually is such that this bath can dissipate the lossescaused by the feasible sources and making themselves felt as generationof heat, without the superconducting state in the accumulator coiland/or in the core thereof breaking down. Such heat sources are inparticular the eddy currents in the superconductors that cannot beeliminated completely, the current heat losses in the metal filaments ofthe coil, the losses, in particular eddy current losses, in the core ofthe coil, the heat generated and finely flowing in the region of currentsupply and current delivery, etc. This holds also for the state in whichthe core material has been transformed into the normally conductingstate.

The laser or maser means mentioned hereinbefore may be disposed in thecore material and shielded in a suitable manner from the superconductorsof the coil proper, so that this means during operation thereof does notimpair the superconducting state of the coil material.

The energy pulses withdrawn during discharge of the accumulator coil canbe of such short length in time that the deflectional movements of theflexible flow tubes in the superconducting material of the coil properand, possibly, of the core are reduced and losses occurringconcomitantly therewith are lowered thereby.

The accumulator coil according to the invention also is especially wellsuited for supplying current to consumers requiring short-time currentpulses of high energy. Highenergy workpiece processing machines can beindicated as a typical example thereof.

The accumulator coil according to the invention preferably is dischargedwith the aid of one or several superconducting high-current switches.This high-current switch may have superconductors in the form of thinfilms, thin wires or powder in a non-conducting matrix. The switch has ameans through which the superconducting material can be converted fromthe superconducting state into the non-superconducting state and viceversa. Preferably, cooling passages are provided between the layers orwires or powder arrangements, respectively, of the superconductingmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and further developments of the invention will now beelucidated in more detail on the basis of embodiments shownschematically in the drawings, in which

FIG. 1 shows a perspective view of a part of a toroidal accumulatorcoil;

FIG. 2 shows a cross-sectional view of an accumulator coil, for instancea cross-section along the line II--II in FIG. 1, having asuperconducting coil core;

FIG. 3 shows the electrical connection of coil segments during chargingof the accumulator coil;

FIG. 4 shows the electrical connection of coil segments of theaccumulator coil during discharge;

FIG. 5 shows a cross-sectional view of an accumulator coil, for instancealong the line II--II in FIG. 1, for schematically illustrating theintroduction of magnetic flow quanta in the accumulator coil.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The accumulator coil 2 shown in FIG. 1 is of toroidal configuration andhas a round, circular torus cross-section according to II--II. Thesupporting structure of the accumulator coil 2 consists of insulatormaterial and can be illustrated geometrically as a hollow cylinder bentinto a circular shape. The supporting structure can be designed as shownmore clearly by the embodiment according to FIG. 2.

On the supporting structure, along the toroidal ring, there are disposedsuccessive coil segments 4 which, when seen per se, are of circularconfiguration each. These coil segments are wound, for instance, fromvery thin filament wires or composed with a radially successive layersequence of insulating material and conducting material, cp. also theembodiment according to FIG. 2. The coil segments 4 are connected toeach other in an electrically conducting manner, the type of connectionbeing elucidated in more detail hereinafter.

The current conductors of the coil segments 4 consist of superconductingmaterial, preferably high-temperature superconducting material. Eitherthe entire accumulator coil 2 is disposed in a bath of liquid heliumor--in the case of high-temperature superconductors--in a bath of liquidnitrogen. Or cooling of the superconductors is carried out by means ofsmaller cooling spaces having liquid helium or liquid nitrogen flowingtherethrough, as illustrated for instance in the embodiment according toFIG. 2. Connections to an external primary charging circuit and to anexternal secondary discharging circuit are provided, but not shown inthe drawings.

FIG. 2 illustrates a preferred structure of a coil segment 4 in moredetail. Reference numeral 6 designates the insulating supportingstructure generally outlined hereinabove. Disposed thereon is asuperconducting ring 8, for instance in the form of a thin filmevaporated thereon, or of a ceramic layer applied in a different manner,or of a ring remainder left standing from a coating of superconductingmaterial previously applied along the accumulator coil 4 in continuousmanner. Radially outside of the ring 8, there is provided an annular orcylindrical coolant space 10 having liquid helium or nitrogen flowingtherethrough.

The structure described is repeated once more or several times more in amanner progressing radially outwardly. On the very outside, theoutermost coolant space 10 is enclosed by a housing 12.

The superconducting rings 8 can be electrically connected individually.However, it is for instance possible as well to electrically interrupteach superconducting ring 8 at a peripheral location and to electricallyconnect the individual interrupted rings in such a manner that, so tospeak, a coil with radially successive windings is simulated.

Inside of the supporting structure 6 there are provided carrierinsulators 14 of segment shape in the cross-section shown. Between thetwo carrier insulators 14, there is located a core 13 which, in a mannerquite similarly to the structure of the coil segments 4 proper, is alayer sequence of insulator layers 16, very thin superconducting layers18 and of flat cooling spaces 20 having liquid helium or liquid nitrogenflowing therethrough.

Instead of the described layer structure of the coil segments 4 ofinsulator material 6 and superconducting material 8, it is also possibleto provide a coil segment 4 wound from very thin superconductingfilament wires, possibly in more or less strictly alternating mannerwith very thin, normal-conduction metal filaments. FIGS. 3 and 4illustrate the manner of interconnection of the individual coil segments4 which together constitute the toroidal accumulator coil 2. Duringcharging, a series connection of the coil segments is preferred (FIG.3), whereas during discharge of the accumulator coil 4 a parallelconnection of the individual coil segments 4 is preferred (FIG. 4).FIGS. 3 and 4 also reveal the ends of the primary circuit 22 and of thesecondary circuit 24.

During discharge, electrical energy pulses of very short duration aresupplied from accumulator coil 2 to the current consumer (not shown). Toproduce the pulses, a pulse discharge circuit 32 is provided insecondary circuit 24. One or more superconducting high-current switchesmay be included in discharge circuit 32. Energy pulses of less than 10ms duration are especially suitable, with pulses shorter than 5 ms beingpreferred and with pulses shorter than 1 ms being better still. This isespecially well suited for supplying current to consumers requiringshort-duration current pulses of high energy, such as high-energyworkpiece processing machines. The withdrawal of energy in very briefpulses from an accumulator coil 2 with very thin superconductors has theadded benefits that deflectional movements of the flow tubes in thesuperconducting material are reduced and eddy current losses areextremely low.

When no separate coil segments 4 are provided for charging anddischarging the accumulator coil 2, it is favorable to design theconnection of the coil segments 4 such that is possible to change from aseries connection to a parallel connection and vice versa. It is to beunderstood that the connection may also be designed such that duringdischarge selectively either all or only a smaller or larger part of thecoil segments 4 is directly employed, for instance only every second orevery third coil segment 4, so that the current load along the torus isevenly distributed.

In case the accumulator coil is not of toroidal configuration, as shown,but of solenoid configuration, the torus has to be conceived as beingcut open at one location and being brought into a rectilinear shape.

FIG. 5 schematically illustrates a further preferred possibility ofcharging the accumulator coil 2. A superconducting platelet 26, which isvery thin in accordance with the superconductor thickness and whoseplane extends perpendicularly to the axis of the torus ring, projectsradially outwardly beyond the respective coil segment 4. A ring 28 ofmagnets can be rotated concentrically with respect to the axis 30 of thetorus ring. In front of the drawing plane of FIG. 5 the ring of magnetshas a series of permanent-magnet north poles which are circumferentiallyspaced, and to the rear of the drawing plane of FIG. 5 it has a seriesof permanent-magnet south poles which are circumferentially distributedin the same manner. Each time such a pair of north pole and south polepasses the platelet 26 with a slight air gap therebetween, magnet quantaare deposited on the platelet 26 and migrate into the coil segment 4electrically connected to the platelet 26. In this way, the respectivecoil segment 4 can be charged in a time-spread manner. An accumulatorcoil of solenoid configuration can be charged in a quite analogousmanner, with the ring 28 of magnets rotating about the rectilinearsolenoid axis.

With the toroidal accumulator coil 2 shown, the illustrated ring 28 ofmagnets, as an alternative, may be designed to rotate along the torus,i.e. about an axis perpendicular to the drawing plane of FIG. 5 andextending through the center of the torus ring. In this case, theplatelet 26 would have to be conceived as being tilted upwardly in FIG.5 by 90°; the north poles would be located above the platelet 26 and thesouth poles therebelow.

What is claimed is:
 1. A process for supplying a current consumer withcurrent, comprising the steps of:storing energy in a superconductingaccumulator coil having thin superconductors; and electricallyconnecting the accumulator coil to the current consumer via at least oneswitch which is opened and closed at high frequency to supply thecurrent consumer with DC pulses of high power and short duration.
 2. Aprocess according to claim 1, wherein the pulse duration of the DCpulses is less than 10 ms.
 3. A process according to claim 2, whereinthe pulse duration of the DC pulses is less than 5 ms.
 4. A processaccording to claim 3, wherein the pulse duration of the DC pulses isless than 1 ms.
 5. A current accumulator for accumulating electricalenergy and for supplying a current consumer with electrical current,comprising:a superconducting accumulator coil having thinsuperconductors; and pulse discharge means for selectively connectingthe accumulator coil to the current consumer to supply the currentconsumer with DC pulses of high energy and short duration, the pulsedischarge means including at least one switch which is opened and closedat high frequency and which electrically connects the accumulator coilto the current consumer when that at least one switch is closed.
 6. Acurrent accumulator according to claim 5, wherein the superconductorsare high-temperature superconductors having a transition temperature ofat least about 80° K.
 7. A current accumulator according to claim 5,wherein the superconductors having a diameter of less than 20 μm.
 8. Acurrent accumulator according to claim 5, wherein the superconductorsare provided in the form of layers, each having a layer thickness ofless than 20μm.
 9. A current accumulator according to claim 5, whereinthe superconductors are formed from a layer applied across a large area,by local mechanical removal of material from the layer.
 10. A currentaccumulator according to claim 5, wherein, when viewing the accumulatorcoil cross-section, several superconductor layers are provided followingeach other in the radial direction.
 11. A current accumulator accordingto claim 10, wherein the accumulator coil additionally comprisesinsulating intermediate layers, and wherein the superconductor layersare formed successively, with an insulating intermediate layer beingprovided therebetween, and are each electrically terminated.
 12. Acurrent accumulator according to claim 5, wherein the accumulator coilcomprises wound, thin, superconducting filament wires.
 13. A currentaccumulator according to claim 12, wherein the accumulator coil furthercomprises thin normal-conduction wires, and wherein the superconductingfilament wires are provided substantially in an alternating manner withthe thin normal-conduction metal wires.
 14. A current accumulatoraccording to claim 5, wherein the accumulator coil comprises a pluralityof successive coil segments in the longitudinal direction thereof.
 15. Acurrent accumulator according to claim 14, wherein the coil segments areindividually prefabricated and are then joined to form the accumulatorcoil.
 16. A current accumulator according to claim 14, wherein the coilsegments are magnetically coupled.
 17. A current accumulator accordingto claim 14, wherein the coil segments are connected in such a mannerthat the accumulator coil can be charged in a series connection of thecoil segments and discharged in a parallel connection of all of the coilsegments.
 18. A current accumulator according to claim 5, wherein theaccumulator coil is of toroidal configuration.
 19. A current accumulatoraccording to claim 5, wherein the accumulator coil is connected to aprimary circuit for charging.
 20. A current accumulator according toclaim 5, further comprising charging means for charging the accumulatorcoil by introducing magnetic flow quanta according to the flow pumpprinciple.
 21. A current accumulator according to claim 5, furthercomprising charging means for charging the accumulator coil, thecharging means including means for producing a pulsating DC magneticfield.
 22. A current accumulator according to claim 21, wherein theaccumulator coil is toroidal and wherein the means for producing apulsating DC magnetic field comprises a rotatable magnet ring havingpermanent magnets.
 23. A current accumulator according to claim 21,wherein the means for producing a pulsating DC magnetic field comprisesa current conductor which produces a pulsating field, the accumulatorcoil being charged by induction.
 24. A current accumulator according toclaim 5, wherein the ratio between the radial thickness of the spaceequipped with superconductors and the accumulator coil diameter issmall.
 25. A current accumulator according to claim 5, wherein theaccumulator coil comprises a core composed of superconducting material.26. A current accumulator according to claim 25, further comprises statetransition means for altering the current intensity in the accumulatorcoil by causing a transition of the superconducting material of the corefrom the superconducting state to the normal-conduction state and viceversa.
 27. A current accumulator according to claim 26, wherein thestate transition means comprises means for applying a magnetic field tothe core.
 28. A current accumulator according to claim 5, wherein theaccumulator coil comprises at least one superconducting discharging coilmagnetically coupled to the superconductors.
 29. A current accumulatoras claimed in claim 5, wherein the superconductors are less than about20 μm thick and wherein each pulse has a duration of less than about 10ms.
 30. A current accumulator according to claim 5, wherein thesuperconductors are formed by local etching from a layer applied acrossa wide area.
 31. A current accumulator according to claim 14, whereinthe coil segments are connected in such a manner that the accumulatorcoil can be charged in a series connection of the coil segments anddischarged in a parallel connection of some of the coil segments.
 32. Acurrent accumulator according to claim 5, wherein the accumulator coilis of solenoid configuration.
 33. A current accumulator according toclaim 26, wherein the state transition means comprises means forintroducing a current pulse into the core.
 34. A current accumulatoraccording to claim 26, wherein the state transition means comprisesmeans for irradiating a radio-frequency field into the core.
 35. Acurrent accumulator according to claim 26, wherein the state transitionmeans comprises means for irradiating thermal radiation in the core. 36.A current accumulator according to claim 26, wherein the statetransition means comprises means for subjecting the core to theinfluence of a laser beam.
 37. A current accumulator according to claim26, wherein the state transition means comprises means for subjectingthe core to the influence of a maser beam.